Protein kinases are a class of proteins that regulate a variety of cellular functions. This is accomplished by the phosphorylation of specific amino acids on protein substrates resulting in conformational alteration of the substrate protein. The conformational change modulates the activity of the substrate or its ability to interact with other binding partners. The enzyme activity of the protein kinase refers to the rate at which the kinase adds phosphate groups to a substrate. It can be measured, for example, by determining the amount of a substrate that is converted to a product as a function of time. Phosphorylation of a substrate occurs at the active-site of a protein kinase.
The JNK (Jun N-terminal kinase) protein kinases (also know as "stress-activated protein kinases" or "SAPK") are members of the mitogen-activated protein (MAP) kinases. See, e.g., S. Gupta et al., EMBO J., vol. 15 no. 11 (1996) pp. 2760-2770; and Yang et al., Nature, vol. 389 (Oct. 23, 1997) pp. 865-870. At least ten JNK isoforms are currently known. See, Gupta, id. As its name indicates, one of the substrates for JNK is c-Jun. JNK phosphorylates the NH.sub.2 -terminal activation domain of c-Jun on Ser63 and Ser73, causing increased c-Jun transcriptional activity. See Gupta, id. In turn, c-Jun is an AP-1 transcription factor that mediates immediate-early gene expression. See, e.g., A. Minden et al., Biochimica et Biophysica Acta 1333 (1997) F85-F104; and A. Karin, Biochimica et Biophysica Acta, vol.172 (1991) pp.129-157.
The JNK protein kinase is markedly activated in response to treatment of cells with pro-inflammatory cytokines or exposure to environmental stress. JNK thus mediates the effect of extracellular stimuli on c-Jun. See Gupta, supra; and Minden, supra. Accordingly, JNK is a physiological regulator of AP-1 transcriptional activity. Thus, inhibition of JNK activity will inhibit AP-1-dependent transcription of inflammatory and immune mediators which are implicated in pathological proliferative conditions, for example inflammatory diseases and neuro-degenerative diseases, in particular, rheumatoid arthritis. See, e.g. Swantek et al., Molecular and Cellular Biology, vol. 17 (1997) pp. 6274-6282; Maroney et al., J. Neuroscience, vol. 18 (Jan. 1, 1998) pp. 104-111; and Minden, supra, at F92.
The rat homologue of JNK is also called SAPK (stress-activated protein kinase). SAPK isoforms share significant (&gt;90%) sequence identity with the corresponding JNK isoforms [compare Kyriakis et al., Nature, Vol. 369 (May 12, 1994) pp. 156-160 and Gupta et al., supra]. Both JNK and SAPK are capable of phosphorylation of the c-Jun substrate and thus have very similar enzyme activity. JNK and SAPK are part of a protein kinase cascade that is activated by various extracellular stimuli. See e.g. Minden supra; and Kyriakis et al., BioEssays Vol. 18 (1996) pp. 567-577. JNK and SAPK each can be activated by phosphorylation on specific threonine and tyrosine residues by dual specificity MAP kinase kinases such as MKK4, SEK-1, or MKK7. See Kyriakis et al., supra; and Tournier et al., Proceedings of the National Academy of Sciences USA Vol. 94 (July 1997), pp. 7337-7342). The dual specificity MAP kinase kinases can be activated by phosphorylation on serine and/or threonine residues by MAP kinase kinase kinases such as MEKK-1. Thus, measurement of JNK or SAPK enzyme activity may be enhanced by activation by the upstream or preceding kinases. Moreover, measurement of SAPK inhibition closely correlates with JNK inhibition.
Inhibitors of protein kinase catalytic activity are known in the art. See U.S. Pat. No. 5,792,783 (3-heteroaryl-2-indolinones that modulate/inhibit tyrosine kinase signal transduction); WO 98/24432 (indoline compounds that inhibit FLK protein kinase); WO 97/45409 (substituted tetralylmethelen-oxindole analogues that inhibit tyrosine kinase). In particular, small molecule inhibitors typically block the binding of substrates by tightly interacting with the protein kinase ATP binding site (or "active site"). See WO 98/24432. It is desirable to identify small-molecule compounds that may be readily synthesized and are effective in inhibiting the catalytic activity of protein kinases, in particular of the JNK protein kinases.
Indolinone (also known as oxindole) compounds asserted to be useful in the regulating abnormal cell proliferation through tyrosine kinase inhibition are disclosed for example in WO 96/40116, WO 98/07695, WO 95/01349, WO 96/32380, WO 96/22976, WO 96/16964, WO 98/50356 (2-indolinone derivatives as modulators of protein kinase activity); Mohammadi et. al, Science, Vol. 276, May 9, 1997, pp. 955-960. Oxindole derivatives have also been described for various other therapeutic uses: U.S. Pat. No. 5,206,261 (improvement of cerebral function); WO 92/07830 (peptide antagonists); EP 580 502 A1 (antioxidants).
There continues to be a need for easily synthesized, small-molecule compounds effective in inhibiting JNK protein kinase and thus useful in the treatment or control of pathological proliferative conditions, for example inflammatory diseases and neuro-degenerative diseases, in particular, rheumatoid arthritis. It is thus an object of this invention to provide such compounds and compositions containing such compounds.